How to account for service fees charged by vendor

I am trying to figure out how to deal with the following transaction.

I receive a referral commission from a vendor per customer referred.

I created a service commission item and then and invoice to the vendor with the item listed.

The vendor paid us via automated deposit, and the transaction on the bank is showing a deposit for 

the commission amount that we've invoiced for and also a debit amount charged by the vendor to cover

their processing fees.

How do I account for the debited vendor fees?